The invention relates to improvements in the structure by which a load-handling attachment is removably mounted upon a lift truck carriage so as to permit quick mounting or demounting of the attachment. Such mounting or demounting of load-handling attachments is a common occurrence in the materials handling industry, owing to the different nature of various types of loads to be handled each requiring different load-handling apparatus such as load forks, paper roll clamp, carton clamp, push-pull attachment etc. Since a lift truck is a highly versatile machine capable of handling any of such loads depending upon the load-handling attachment with which the truck is equipped, standardized mating assemblies to facilitate quick interchangeability of load-handling attachments are provided on the front surface of lift truck load carriages and on the rear surface of load-handling attachments. These take the form of upper and lower horizontal bars on the front of the lift truck carriage, having upwardly and downwardly protruding lips respectively, which matingly engage upper and lower hook assemblies mounted on the rear of the load-handling attachment. The upper hook assembly is normally fixed permanently and immovably to the load-handling attachment, making it necessary that the lower hook assembly, normally comprising a pair of transversely-spaced hooks, be removably mounted to the rear of the load-handling attachment by bolts. During mounting of the attachment, after the upper hook assembly has engaged the upper bar of the load carriage the lower hooks can be bolted into place on the rear side of the downwardly-protruding lip of the lower carriage bar. For demounting, conversely, the lower hooks are unbolted and removed first.
The removable lower hooks currently used on load-handling attachments have certain significant drawbacks. One such disadvantage stems from the detachability of the hooks and bolts from the load-handling attachment, creating loose parts which may easily become misplaced or separated from their attachments during an attachment exchange procedure, particularly if there is any substantial time lapse between the demounting and remounting of a particular attachment.
A further disadvantage of most lower hooks is the requirement for tools (i.e. wrenches) to remove and attach the hooks, which tools may not be readily available at the time and place where needed thereby causing delay and resultant lost production time for the lift truck. Some lower hook assemblies have been devised wherein the hooks may be rotated from positions engaging the lower carriage bar downwardly to disengaged positions, without requiring removal of the hooks, by removing a slidable pin which locks the rotatable hooks in the engaged position. However, the removable pin suffers from the disadvantages outlined in the previous paragraph in that it is a loose part which may easily become displaced or separated from the attachment.
In addition, both the removable hooks and those featuring removable pins are susceptible to negligence on the part of a workman during mounting of an attachment in that it is possible to place the hooks in their engaged positions without it being necessarily noticeable that the hook bolts are not tightened sufficiently or that a removable pin has not been inserted properly. Accordingly the hook and/or removable pin may be able to work itself loose without detection during subsequent operation of the attachment due to repeated vibrations, and impacts.